1. Field of the Invention
The present invention relates to a water electrolysis system having a water electrolysis apparatus which includes an electrolyte membrane and current collectors disposed on respective opposite sides of the electrolyte membrane, providing anodes and cathodes, wherein the water electrolysis apparatus electrolyzes water to generate oxygen on the anodes and hydrogen on the cathodes, and a casing which has a chamber accommodating the water electrolysis apparatus therein, and a method of operating such a water electrolysis system.
2. Description of the Related Art
Solid polymer electrolyte fuel cells generate DC electric energy when anodes thereof are supplied with a fuel gas, i.e., a gas mainly composed of hydrogen, e.g., a hydrogen gas, and cathodes thereof are supplied with an oxygen-containing gas, a gas mainly composed of oxygen, e.g., air.
Generally, water electrolysis apparatus are used to generate a hydrogen gas for use as a fuel gas for such solid polymer electrolyte fuel cells. The water electrolysis apparatus employ a solid polymer electrolyte membrane (ion exchange membrane) for decomposing water to generate hydrogen (and oxygen). Electrode catalyst layers are disposed on the respective sides of the solid polymer electrolyte membrane, making up a membrane electrode assembly. Current collectors are disposed on the respective opposite sides of the membrane electrode assembly, making up a unit. The unit is essentially similar in structure to the fuel cells described above.
A plurality of such units are stacked, and a voltage is applied across the stack while water is supplied to the current collectors on the anode side. On the anodes of the membrane electrode assembly, the water is decomposed to produce hydrogen ions (protons). The hydrogen ions move through the solid polymer electrolyte membranes to the cathodes, where the hydrogen ions combine with electrons to generate hydrogen. On the anodes, oxygen generated together with hydrogen is discharged with excess water from the units.
U.S. Pat. No. 5,980,726, for example, discloses a hydrogen producing system as a water electrolysis system incorporating such a water electrolysis apparatus. As shown in FIG. 8 of the accompanying drawings, the disclosed hydrogen producing system includes a casing 1 whose internal space is divided into a zone A and a zone B by a wall 1a. The zone A accommodates therein an electric power supply unit 2, a heat exchanger 3, a fan 4, and a blower 5, etc., whereas the zone B accommodates therein a cell stack 6 and a hydrogen drier 7, etc.
When the fan 4 is actuated, it introduces external air into the zone A to cool the heat exchanger 3 and the electric power supply unit 2 and also to keep the zone A under a positive pressure. When the blower 5 is actuated, it introduces heated clean air from the zone A into the zone B, keeping the zone B under a pressure which prevents external air from entering the zone B.
The zone A is kept under the positive pressure to prevent a hydrogen gas from flowing into the zone A. Usually, the zone A houses therein various electric components such as the electric power supply unit 2 and the like that need to be isolated from a hydrogen gas atmosphere.
The electric components housed in the zone A include electric components which are susceptible to noise and electric components which tend to generate high-level noise. Since it is not desirable to have these electric components placed altogether in the zone A for their desired performance, it is necessary to divide the zone A into a plurality of compartments which are associated with respective blowers 5 and place the electric components separately in the compartments. However, such a zone structure is complex and uneconomical.